Inorganic phosphate corrosion resistant coatings

ABSTRACT

This disclosure relates to compositions for protecting a metallic surface susceptible to corrosion, the composition comprising a first component comprising an aqueous mixture of an acid-phosphate of chemical formula A m (H 2 PO 4 ) m .nH 2 O, where A is hydrogen ion, ammonium cation, metal cation, or mixtures thereof where m=1-3, and n=0-6; the first component solution adjusted to a pH of about 2 to about 5, the first component having a particle size distribution between 0.04 to 60 micron; and a second component, configured for combination and at least partial reaction with the first component to provide a phosphate ceramic, the second component comprising an aqueous solution or suspension of an alkaline oxide or alkaline hydroxide represented by B 2m O m B(OH) 2m , or mixtures thereof, where B is an element of valency 2m (m=1, 1.5, or 2) the second component solution adjusted to a pH of between 9-14.

TECHNICAL FIELD

This disclosure relates to coatings comprising acid-phosphate andalkaline metal oxide/hydroxide components that inhibit corrosion ofmetals, and specifically, the manufacture and method of coatingphosphate ceramics on metal.

BACKGROUND

Corrosion of structural steel and other metals is a serious problem inconstruction and utility industry. When exposed to humid and salineenvironments, especially at elevated temperatures, steel deteriorates.To minimize or reduce the extent of this corrosion, alloys of steel,such as galvanized (zinc coated) compositions, or chrome platedcompositions are used. While this approach may solve the problem in theshort run, the problem persists when the steel is exposed to theabove-mentioned environments over long periods of time. This inventiondiscloses uniquely-suited phosphate-based composite coatings thatminimize or reduce the corrosion of steel or other metals and make itunnecessary to use alloys of steel such as galvanized (zinc coated)compositions or chrome plated compositions.

Phosphating to passivate a steel surface is generally known in the steelindustry. Typically, well polished steel is immersed in phosphate bathof pH between 4-4.5 containing 2-3 g/L phosphoric acid, 2-3 g/L ofammonium or zinc dihydrogen phosphate as buffer, and a small amount(<0.5 g/L) of oxidizer, to produce an iron phosphate passivation layer.In the process, however, hydrogen gas is liberated by the reaction ofelemental iron with water in the extremely acidic environment. Thisproduces a very thin passivation layer that is porous and not abrasionresistant, and as a result, an additional coating is required to makethe surface of the passivated steel inaccessible to atmospheric oxygenand/or abrasion resistant. This process has, therefore, at least thefollowing disadvantages: (i) an acid immersion bath/tank, whichgenerates sludge as formed by accumulating reaction products—making thebath less effective and creating environmental disposal issues for thesludge and the acidic solution; (ii) oxidizers used in the passivationprocess produce toxic gases. For example, chlorates produce chlorine,meta nitro benzene sulfonic acid produces nitrous oxide, potassiumpermanganate presents occupational health risks; (iii) resultantpassivation layers are not abrasion resistant, therefore, abrasionresistance must be augmented by additional coating(s).

SUMMARY

In a first embodiment, a phosphate ceramic precursor composition isprovided. The composition comprising a first component comprising anaqueous mixture of an acid-phosphate of chemical formulaA^(m)(H₂PO₄)_(m).nH₂O, where A is hydrogen ion, ammonium cation, metalcation, or mixtures thereof; where m=1-3, and n=0-6; the first componentsolution adjusted to a pH of about 2 to about 5, the first componenthaving a particle size distribution between 0.04 to 60 micron; and asecond component, configured for combination and at least partialreaction with the first component to provide a phosphate ceramic, thesecond component comprising an aqueous mixture of an alkaline oxide oralkaline hydroxide represented by B^(2m)O_(m), B(OH)_(2m), or mixturesthereof, where B is an element of valency 2m (m=1, 1.5, or 2) the secondcomponent solution adjusted to a pH of between 9-14.

In a first aspect of the first embodiment, about 50 percent of theparticle size distribution of the first component is particles having aparticle size less than 50 microns, less than 40 microns, less than 30microns, or less than 20 microns. The minimum of particle sizes beingabout 0.04 micron, about 0.4 micron, or about 4 micron.

In a second aspect, alone or in combination with any one of the previousaspects of the first embodiment, about 90 percent of the particle sizedistribution of the first component is particles having a particle sizeless than 50 microns, less than 40 microns, or less than 30 microns.

In a third aspect, alone or in combination with any one of the previousaspects of the first embodiment, the first component average particlesize is about 20 microns to about 30 microns.

In a fourth aspect, alone or in combination with any one of the previousaspects of the first embodiment, the first component comprises at leastone of mono potassium phosphate and mono calcium phosphate, water, andoptionally about 2 to about 10 wt. % phosphoric acid.

In a fifth aspect, alone or in combination with any one of the previousaspects of the first embodiment, the second component is at least one ofmagnesium oxide, calcium oxide, magnesium hydroxide, and calciumhydroxide, and water.

In a sixth aspect, alone or in combination with any one of the previousaspects of the first embodiment, the composition further comprising atleast one corrosion inhibitor precursor of a mineral silicate,wollastonite, talc, amorphous magnesium silicate, amorphous calciumsilicate, diatomaceous earth, silicon dioxide, and amorphous silicondioxide.

In a seventh aspect, alone or in combination with any one of theprevious aspects of the first embodiment, either of the first componentor the second component is present in an amount of at least about 60 wt% to about 80 wt %.

In an eighth aspect, alone or in combination with any one of theprevious aspects of the first embodiment, the composition furthercomprising further comprising a rheology modifier/suspending agent, therheology modifier/suspending agent is at least one of guar gum, diutangum, welan gum, and xanthan gum present in an amount of 0.15-15 weightpercent.

In a second embodiment, a method of providing corrosion protection to ametal surface is provided. The method comprising contacting a metalsurface with a first component and a second component, in any order orin combination; wherein the first component comprises an aqueous mixtureof an acid-phosphate of chemical formula A^(m)(H₂PO₄)_(m).nH₂O, where Ais hydrogen ion, ammonium cation, metal cation, or mixtures thereof;where m=1-3, and n=0-6; the first component solution adjusted to a pH ofabout 2 to about 5, the first component having a particle sizedistribution between 0.04 to 60 micron; and wherein the second componentcomprises an aqueous mixture of an alkaline oxide or alkaline hydroxiderepresented by B^(2m)O_(m), B(OH)_(2m), or mixtures thereof, where B isan element of valency 2m (m=1, 1.5, or 2) the second component solutionadjusted to a pH of between 9-14.

In a first aspect of the second embodiment, about 50 percent of theparticle size distribution of the first component is particles having aparticle size less than 50 microns, less than 40 microns, less than 30microns, or less than 20 microns.

In a second aspect, alone or in combination with any one of the previousaspects of the second embodiment, about 90 percent of the particle sizedistribution of the first component is particles having a particle sizeless than 50 microns, less than 40 microns, or less than 30 microns.

In a third aspect, alone or in combination with any one of the previousaspects of the second embodiment, the first component average particlesize is about 20 microns to about 30 microns.

In a fourth aspect, alone or in combination with any one of the previousaspects of the second embodiment, the first component comprises at leastone of mono potassium phosphate and mono calcium phosphate, water, andoptionally about 2 to about 10 wt % phosphoric acid.

In a fifth aspect, alone or in combination with any one of the previousaspects of the second embodiment, the second component is at least oneof magnesium oxide, calcium oxide, magnesium hydroxide, and calciumhydroxide, and water.

In a sixth aspect, alone or in combination with any one of the previousaspects of the first embodiment or the second embodiment, furthercomprising at least one of a mineral silicate, wollastonite, talc,amorphous magnesium silicate, amorphous calcium silicate, diatomaceousearth, silicon dioxide, and amorphous silicon dioxide.

In a seventh aspect, alone or in combination with any one of theprevious aspects of the second embodiment, either of the first componentor the second component is present in an amount of at least about 60 wt% to about 80 wt %.

In an eighth aspect, alone or in combination with any one of theprevious aspects of the second embodiment, further comprising furthercomprising a rheology modifier/suspending agent, the rheologymodifier/suspending agent is at least one of guar gum, diutan gum, welangum, and xanthan gum present in an amount of 0.15-15 weight percent.

In a ninth aspect, alone or in combination with any one of the previousaspects of the second embodiment, a product produced by the method isprovided.

In a third embodiment, an inorganic phosphate compound is provided ofthe general formula:

-   -   i) B^(s)(A_(3-m)PO₄)_(s); wherein A has a valency of m=1 or 2;        and B has a valency of s=1, or 2;    -   ii) B^(s)(A_((2/m))PO₄)_(s); wherein A has a valency of m=1 or        2; B has a valency of s=1, or 2;    -   iii) ^((2/m))A₃B_(m)(PO₄)₂; wherein A has a valency of m=1 or 2;        ; B has a valency of 3; or    -   iv) B(AOPO₄)_(s); wherein A has a valency of 4 and s=1 or 2; and        B has a valency of 1, or 2;

In a first aspect of the third embodiment, the inorganic phosphate i-ivhas less than 0.000001 to 10 percent of unreacted, crystalline inorganicacid phosphate of an average particle size greater than about 60microns.

In a second aspect, alone or in combination with any one of the previousaspects of the third embodiment, the inorganic phosphate is at least oneof the following: MgKPO₄; Mg(ZnPO₄)₂ Mg(K₂PO₄)₂; Mg₂KPO₄; Mg(ZnPO₄)₂;Mg(K₂PO₄)₂; Al₂Mg₃(PO₄)₂; Mg(ZrOPO₄)₂; Mg[Zr(OH)₂PO₄)₂]₂; andcalcium/magnesium phosphate.

In a third aspect, alone or in combination with any one of the previousaspects of the third embodiment, less than 0.000001 to 10 percent of theunreacted, crystalline inorganic acid phosphate is of an averageparticle size distribution greater than about 50 microns, less than 40microns, or less than 30 microns.

In a fourth aspect, alone or in combination with any one of the previousaspects of the third embodiment, the inorganic phosphate has a densityless than 1 8 g/cm³ or less than 1.5 g/cm³.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a corrosion protection layer of a phosphateceramic coating composition.

FIG. 2 is an illustration of a corrosion protection layer of a phosphateceramic coating composition as disclosed and described herein.

DETAILED DESCRIPTION

In general, disclosed herein are multi-component formulations comprisingat least one acidic phosphate first component and at least one alkalinesecond component, the first and second components being suitable forproviding, upon combination, an inorganic phosphate composition.

As used herein, the phrase “aqueous mixture” refers to a combination ofat least a quantity of water and at least one of the sparingly solubleacid phosphate or basic component. For example, the aqueous mixture cancontain mostly water and suspended, dispersed, or slurried components,and may also contain non-aqueous components such as alcohols and othersolvents. Preferably, water is the major liquid phase. The amount ofsolids (e.g., the sparingly soluble acid phosphate or basic componentand/or other solids) present in the aqueous mixture can be between 1 wt.% to about 80 wt. %, preferably 50-80 wt. % solids.

As used herein, the phrases “sparingly soluble acidic phosphatecomponent” and “acidic phosphate precursor” and “acid component” and“acid-phosphate component” and “Part A” are used interchangeably unlessotherwise indicated. As used herein, the phrase “sparingly solubleacidic phosphate component” refers to inorganic acid-phosphates ofchemical formula A^(m)(H₂PO₄)_(m).nH₂O, where A is metal cation, ormixtures thereof; where m=1-3, and n=0-6. Such inorganic phosphatestypically have low solubility constants characteristic of low aqueoussolubility, e.g., solubility constants (Ksp) of at least 10⁻⁶, 10⁻⁷,10⁻⁸, 10⁻⁹ or smaller. In one aspect, the phrase “sparingly solubleacidic phosphate component” excludes phosphoric acid or ammoniumphosphates, however, non-stoichiometric amounts (e.g., less than 10weight percent to that of the acid phosphate component) of phosphoricacid can be used to adjust pH of the aqueous phosphate precursorcompositions. Because solubility product constants may be pH dependent,the above phrase includes the addition of small amounts of phosphoricacid to the aqueous mixture of sparingly soluble acidic phosphatecomponent to provide a target solubility product constant relative tothat of the basic component.

As used herein phrases “sparingly soluble basic metal oxide andsparingly soluble basic metal hydroxide component” and “sparinglysoluble basic component” and “sparingly soluble alkaline component” and“sparingly soluble alkaline precursor” are used interchangeably unlessotherwise indicated. The phrases “sparingly soluble basic component” and“sparingly soluble alkaline component” and “sparingly soluble alkalineprecursor” are inclusive of materials that are sparingly soluble, e.g.,have low solubility product constants in aqueous media, e.g., solubilityconstants (Ksp) of at least 10⁻⁶, 10⁻⁷, 10⁻⁸, 10⁻⁹ or smaller. In oneaspect, the phrases “sparingly soluble basic metal oxide and sparinglysoluble basic metal hydroxide component” and “sparingly soluble basiccomponent” and “sparingly soluble alkaline component” and “sparinglysoluble alkaline precursor” are exclusive of materials that are readilysoluble, e.g., have high solubility product constants in aqueous media.In one aspect, the sparingly soluble acid phosphate has a solubilityproduct constant that is greater than the sparingly soluble basiccomponent when used in forming the acid/base phosphate coating.

The uniquely-suited formulations and methods disclosed and describedherein are based in one aspect on acid-base inorganic phosphatecompositions. It is believed that similar principles are applicable forother acid/base pair compositions other than inorganic phosphates.Examples of the inorganic phosphate coatings provided herein include amagnesium potassium phosphate coating, and calcium potassium phosphatecoating. These compositions are disclosed herein for coatings on steels,aluminum, and other metals as corrosion inhibitors. When applied to ametal surface as a paste, spray or vapor coating, the compositions reactdepending on their solubility product constants, e.g., where the moresoluble component (e.g., preferably the acidic component) reacts withions associated with the bulk metallic surface substantially or to anextent before the less soluble component (e.g., the basic component).After reactions of the more soluble component with the ions of the bulkmetallic surface, the second component reacts providing an alloyingsurface zone that is chemically bound to the metallic surface andincludes the reaction products of the ions associated with the metallicsurface (e.g., metal ions), and in combination, the acid/basecomponents, bonding therewith and forming a thin layer/coating to themetallic surface. The bonded layer is hard and inhibits corrosion of themetal surface. A range of phosphate-based formulations may be used tocoat and prevent or minimize the corrosion of metallic surfaces. Themetallic surface can be pristine, polished, and/or contain pre-existingcorrosion. By selecting the acid component and basic component based ontheir solubility in the media used to apply them to the metallicsurface, the aforementioned reaction products form that provide animproved corrosion coating for the bulk metal.

The instant compositions can be configured as atomizible, sprayableinorganic phosphate precursor compositions that can be sprayed at arelatively thin thickness. The compositions can hold high solidscontents and yet still hold the solids until setting and thus avoidingthe solids migrating or dislodging from the point of application, e.g.,down a wall, beam, curved surface, or from a ceiling surface. Such spraycoated phosphate ceramic compositions produce high-strength,rapid-setting phosphate ceramic coatings that provide corrosionprotection and/or be used as an undercoating in combination with apolymeric coating or paint, such as an acrylic- or urethane-basedcoating or paint. In one aspect, said phosphate spray coatingcompositions are suitable for spray coating on metal surfaces, forexample, structural elements such as tanks and other storage structures,as well as chassis of transportation vehicles such as automobiles,trains, cycles, aerospace vehicles, trucks, and buses.

Proper particle size selection of one or more of the precursor materialsprovides improved corrosion protection relative to conventionalphosphate coatings. Proper selection of solubility of one or more of theprecursor materials provides improved corrosion protection relative toconventional phosphate coatings. Dense, hard, large crystals are likelyto go into solution and/or react slower and therefore may not completelydissolve and/or react during the formation the ceramic coating and/orinhibit or alter the formation of the passive layer on the metalsurface. If they remain behind after the coating has set up such dense,hard, large crystals arc likely to cause corrosion if in proximity tothe metal surface. Of course, the use of acid-phosphate precursors thatare completely soluble or are rapidly solubilized cause excessiveexothermic heat generation and/or react violently resulting in poorcoating properties. Thus, the combination of proper particle sizeselection and solubility of one or more of the precursor materials asdisclosed and described herein provides improved corrosion protectionrelative to conventional phosphate coatings. Unreacted crystals of acidphosphate precursor (e.g., first component) that, for example, do notdissolved in the formulation prior to set-up, or do not react with astoichiometric amount of base component will eventually dissolve andleave a void in the coating and/or if in contact with a metal surface,commence with an acid-metal reaction that can lead to pitting and othercorrosion-related issues.

It has now been determined that proper selection of particle sizecommensurate with solubility of the acid-phosphate component precursoreffectively reduces or eliminates corrosion caused by the precursorsthemselves as well as providing an improved corrosion coating for themetal surface.

In one aspect, the average particle size of the acid-phosphate precursormaterial is less than 600 microns. Preferably, the average particle sizeof the acid-phosphate precursor material is less than 60 microns, lessthan 50 microns, less than 40 microns, less than 30 microns, or lessthan 20 microns.

Very small particle size phosphate acid (or acid-phosphate) precursorsare achievable with milling or other commutation techniques alone or incombination with surfactants. The present method is particularlyadvantageous with certain low solubility or “sparingly soluble”components, e.g., monopotassium phosphate (MKP) solid in particulateform.

By way of example, the particle size of the acid-phosphate component candetermine whether the resultant ceramic coating is going to providecorrosion protection or actually contribute to localized corrosion aftercoating. Whatever solid phosphate component is chosen, it is preferredthat it go completely into solution and/or react with the basiccomponent before or during set-up. While some chemistry of the phosphatecomponent and the metal surface is desirable and indeed, beneficial, ifun-reacted phosphate component is localized in the solid ceramic and inproximity to the metal surface, and in this localized environment thebasic component is substantially absent or of a non-stoichiometricamount relative to the acid component, overtime and via egress of water,corrosion and/or pitting of the steel surface will likely result. Thisproblem is exacerbated by the presence of large, unreacted particles(e.g., greater than 70 micron, and especially greater than 100-1000micron average diameter particles) of an acid phosphate componentspresent throughout the hardened ceramic that ultimately react withresidual base and/or water that has seeped into the coating leavingbehind in the ceramic a porous structure that further promotes wateregress. Balancing this is the observation that very small particles ofacid and base components tend to react rather quickly reducing setuptime and shelf-life, which has diverted interest in pursuing extremelysmall particle size formulations without the need for additionalchemistries to retard or otherwise inhibit fast reaction rates andexothermic phenomena that likely would otherwise occur.

The above is schematically depicted in FIG. 1, which depicts aconventional phosphate chemistry formulation having particles of acidcomponent 600 greater than about 70 micron and base component 700combined as a coating 400 on metal surface 500. After set-up and over atime period less than the average useable life of the metal objecthaving the coated surface, the unreacted, crystalline base componentsand the acid components of coating 405 react or dissolve, leaving behindporous voids 650 of approximate size or slightly smaller or larger ofthat of the crystal(s) present at set up. Of particular concern is theacid-phosphate crystals left in proximity 610 to the metalsurface-coating interface, which is capable of undergoing the acid-metalreaction and generating hydrogen gas. These particular localized,unreacted acid-phosphate crystals contribute to pitting 625 and othertypes of corrosion of the metal surface and are undesirable in a coatingdesigned for corrosion protection. It is therefore provided herein in atleast one embodiment of the present disclosure to eliminate or reducethe number of large, unreacted acid-phosphate crystals that can bepresent in the corrosion coating prior to and during setup andsubsequently thereafter.

Thus, as depicted in FIG. 2, the phosphate chemistry formulation of thepresent disclosure, having particles of acid component 602 less thanabout 60 micron, and base component 702 combined and cast as a coating402 on metal surface 500. After set-up and over a time period less thanthe average useable life of the metal object having the coated surface,the unreacted, crystalline base components and the acid components ofcoating 405 react or dissolve, leaving behind significantly smallerporous voids 652 of approximate size to that of the crystal(s) presentat set up or slightly smaller or larger and with substantially lesscrystals present at the metal surface-coating interface so as to preventor eliminate post-coating pitting or other types of corrosion of themetal surface.

In various aspects, a multi-component formulation is provided,comprising at least one acidic component and at least one alkalinecomponent. Both components of the multi-component formulation areprovided as solutions, emulsions, dispersions, pastes, or combinationsthereof. Each of the components can be produced separately and storedseparately, and may be dispensed separately or in combination. Thecomponents ultimately are combined prior to or during application andare allowed to react to form an inorganic phosphate composition.

Thus, in one aspect, a phosphate ceramic precursor composition isprovided comprising a first component comprising an aqueous mixture ofan acid phosphate having a particle size distribution between 0.04 to 60micron. In another aspect, about 50% of the particle size distributionof the first component is particles of less than 50 micron, less than 40micron, less than 30 micron, or less than 20 micron. In another aspect,about 90% of the particle size distribution of the first component isparticles having a particle size less than 40 micron, less than 30micron, or less than 20 micron. In yet another aspect, the firstcomponent average particle size is between about 20 micron to about 30micron. The present coatings provide excellent corrosion resistance andalso improved resistance to pitting and other corrosion relatedphenomenon as well as providing a more dense, less porous phosphateceramic by virtue of the reduction in size of voids typically created bythe post-set reaction and/or dissolution of the acid phosphate crystals.

The phosphate ceramic composition can comprise an acidic phosphatecomponent comprising an aqueous solution, suspension, or slurry of anacid-phosphate, for example, of chemical formula A^(m)(H₂PO₄)_(m).nH₂O,where A is hydrogen ion, ammonium cation, metal cation, or mixturesthereof; where m=1-3, and n=0-6; the first component solution adjustedto a pH of about 2 to about 5; a basic component, comprising, forexample, an aqueous solution, suspension, or slurry of an alkaline oxideor alkaline hydroxide represented by B₂mOm, B(OH)₂m, or mixturesthereof, where B is an element of valency 2m (m=1, 1.5, or 2) the secondcomponent solution adjusted to a pH of between 9-14; and a rheologymodifier/suspending agent in an amount capable of providing shearthinning of either the first component or the second component andfurther capable of suspending a high solids content of either the firstcomponent or the second component for atomization. Optionally, pigmentsand/or aggregate material can be present in an amount in at least one ofthe acidic phosphate and the basic component capable of imparting anobservable color and/or texture. The above composition can be configureas an atomiziblc spray coating that can provide a thin, paint-likecoating for imparting corrosion resistance to metallic surfaces. Therheology modifier/suspending agent can be at least one of guar gum,diutan gum, welan gum, and xanthan gum. By using an optional rheologymodifier/suspending agent in an amount capable of providing shearthinning of the basic component and further capable of suspending a highsolids content of either the acidic component or the basic component foratomization, excellent paint-like coatings for imparting corrosionresistance to metallic surfaces arc obtained.

Processes and articles prepared by coating with the aforementionedformulation are disclosed and described herein and such coated articlesovercome many if not all of the problems related to conventionalpassivation processes of iron, steels, aluminum, and other corrodiblemetals. The instant processes also provide a more economical,environmentally-friendly method of coating steel and other metalsurfaces with acid-base inorganic phosphate based coatings that not onlypassivate the layer but also provide abrasion resistance along with goodaesthetics in one step.

The instant coatings disclosed herein can comprise, in part, theformation of poly phosphates, and in particular, poly phosphates formedby phosphites at the interfacial regions of the substrate surface in theinstant coating. Polyphosphate can provide abrasion resistance andimpermeablity to water and humidity, thus improving abrasion resistanceas well as improving corrosion resistance to the substrate surface.

In one aspect, an acid-phosphate composition, one acidic with a pHbetween about 3 to about 4.5, and the other, an alkaline component witha pH between about 10 and about 11. These two components are contactedwith the substrate surface, where they combine form a coating. Forexample, mono potassium phosphate (KH₂PO₄) and a magnesium hydroxide(Mg(OH)₂, or its brine) composition with or without fillers such aswollastonite (CaSiO₃) or fly ash, can be combined and contacted with acorrodible metal surface (e.g., steel). Once the compositions contactthe surface, a coating forms that bonds instantly to the substrate.While not wishing to be held to any particular theory, it is believedthat the contact by the acidic phosphate and an alkaline oxide orhydroxide, or oxide mineral components provides an initial passivationlayer (sub-, primer, or bottom layer) as well as the corrosionprotective layer.

In certain aspects of the present disclosure, the metallic surface isthat of a transition metal or its alloy, for example, iron, chromium,aluminum, copper, etc.

Acidic phosphate component - The acidic phosphate component consists ofan acid-phosphate representative of the formula, A^(m)(H₂PO₄)_(m).nH₂O,where A is an m-valent clement such as sodium (Na, m=1), potassium (K,m=1), magnesium (Mg, m=2), calcium (Ca, m=2), aluminum (Al, m=3) etc. Amay also be a reduced oxide phase when higher-valent oxides are used.For example, for iron, which exists in valence state of +2 and +3 (FeOand Fe₂O₃ as oxides), A can be the metal of lower oxidation state. Itcan also be a cation of oxides of four-valent metal oxide such as ZrO²⁺,in which case m=2. nH₂O in the formula above is simply the bound water,where n can be any number, normally ranging from 0 to 25.

It is possible to use hydro phosphates of trivalent metals such asaluminum, iron and manganese represented by the formula AH₃(PO₄)₂.nH₂O,where A is a transition metal that includes aluminum, iron, manganese,yttrium, scandium, and all lanthanides such as lanthanum, cerium, etc.

In case the pH of the acidic precursor is higher than needed for instantreaction, phosphoric acid may be added and the pH may be adjusted tobring down the pH. A preferred pH selected is between 3 and 4, and themost preferred pH is between 3 and 3.5. either elevating the pH ofphosphoric acid or that of an acid-phosphate such as magnesiumdihydrogen phosphate (Mg(H₂PO₄)₂) or aluminum trihydrogen phosphate(AlH₃(PO₄)₂) by neutralizing partially using an alkaline oxide,hydroxide, or a mineral, or by acidifying a dihydrogen phosphate such asmono potassium phosphate (KH₂PO₄) that has a pH>3.5 by adding a smallbut appropriate amount of phosphoric acid or a low pH acid phosphatesuch as Mg(H₂PO₄)₂ or aluminum trihydrogen phosphate AlH₃(PO₄)₂.Examples described later in this document provide the art of adjustingthis pH.

Often the acid-phosphate solid used as the precursor is only partiallysoluble. In such a case, the acid-phosphate precursor is milled (wet ordry milling or other grinding or size-reduction technique) so that theparticles pass through 325 mesh sieve (less than 50 micron), 400 meshsieve (less than 38 micron), 450 mesh sieve (less than 32 micron), 500mesh sieve (less than 25 micron), or 635 mesh sieve (less than 20micron). In one aspect, the acid phosphate has a solubility productconstant that is greater than the basic component used in forming theacid/base phosphate coating.

Water may be added to the precursor component to reduce the viscositythereof, or other types of viscosity reducing agents may be used.Commercial additives that prevent algae growth may also added to thisprecursor so that no algae growth occurs during storage of thisprecursor.

The Basic component or precursor comprises one or more basic oxides,hydroxides and basic minerals. The basic component generally consists ofa sparsely soluble oxide, or preferably a hydroxide with a solubilityproduct constant less than the acid phosphate precursor. In one aspect,a particle size less than 230 micron or of a size commensurate with thatof the acid component discussed above. The oxide may be represented bythe formula B^(2m)O_(m) or B(OH)_(2m), where B is a 2m-valent metal. Alldivalent metal oxides (m=1), and some trivalent metal oxides in reducedstate fall into this category of small solubility product constantoxides. Examples of divalent oxides are, but not limited to, magnesiumoxide, barium oxide, zinc oxide, calcium oxide and copper oxide.Examples of trivalent oxides in reduced state are iron oxide (FeO), andmanganese oxide (MnO). In preferred aspects of the instant disclosure, 0to about 10 molar excess of basic component relative to acidic componentis used. For example, about 0-10 molar excess of Mg(OH)₂ based on MKPacidic phosphate can be used. In one aspect, the molar ratio ofacid:base components can be between about 0.9:1.0 to about 1.0:3.0;preferably about 1.0:2.0; and most preferably, about 1.0:1.8. Forexample, the composition comprising Mg(OH)₂:KH₂PO₄=1.8:1.0 providesequal volumes of Parts A and B during spraying. In other aspects, spraycoatings of the instant compositions having a molar ratio of about 1:2or about 1:1.5 (acid:base) with mixing, sprayed well and corrosionprotected effectively.

Inorganic Phosphate Coating Compositions

A range of phosphate compositions may be used as the corrosion inhibitorcoatings commensurate with the spirit and scope of that disclosed anddescribed herein, the following three exemplary, non-limiting examplesare provided:

-   -   1. Magnesium potassium phosphate coating formed by the        combination and/or reaction of magnesium oxide (MgO) and mono        potassium phosphate (KH₂PO₄), which in the presence of water        combine to produce magnesium potassium phosphate ceramic,        comprising MgKPO₄.6H₂O. Magnesium potassium phosphate is also        referred to hereafter as “MKP”.    -   2. Magnesium hydrogen phosphate (newberyite) coating formed by        the combination and/or reaction of magnesium oxide (MgO) and        phosphoric acid solution (H₃PO₄ solution), which when mixed well        and allowed to dry, combine to produce a magnesium hydrogen        phosphate coating comprising MgHPO₄.3H2O.    -   3. Magnesium hydrogen phosphate (newberyite) coating formed by        the combination and/or reaction of magnesium dihydrogen        phosphate compositions usually have an aqueous pH between about        2.5 and about 5.0. Magnesium hydrogen phosphate is also referred        to hereafter as “MHP”. MHP solutions with a pH of about 3 or        slightly higher are generally believed more effective in the        production of corrosion resistant products and, for at least        that reason, tend to be preferred.

Under ambient conditions, aqueous mixtures of magnesium potassiumphosphate compositions and magnesium hydrogen phosphate compositionsexhibit a paste-like consistency that can be shear thinned to beatomizable for spraying. When these compositions are applied to asurface, e.g., steel, as coatings, it is believed that one or morereaction occurs, and/or the one or more reaction occur at differentrates, and a thin layer of the above compositions bonds to the metallicsurface. The remaining parts of the coatings distal from the metallicsurface can be loosely bound and can be easily scraped off, but thelayer or coating is thin it remains and is very hard, resistant toabrasion, and inhibits corrosion of the surface. Thus, in one aspect,this thin layer provides protection of the metallic surface fromcorrosion. Similar results are observed when these compositions areapplied to the surface of other metals besides steel, such as aluminum.It is believed that the same effects would be observed for copper,nickel, tungsten, vanadium and other transition metals prone tooxidation at pH's of between about 2 to about 11, and potentials ofabout 2 eV to about −2 eV.

In another aspect, the above phosphate ceramic precursor components areutilized to form an inorganic phosphate compound. The inorganicphosphate compound comprises less than 1%, less than 0.1%, less than0.01%, less than 0.001%, less than 0.0001%, less than 0.00001%, lessthan 0.000001% unreacted, crystalline inorganic acid phosphate of anaverage particle size greater than about 60 micron, 50 micron, 40micron, 30 micron, or 20 micron. Residual unreacted inorganic acidphosphate can be determined using a number of techniques including butnot limited to x-ray crystallography, Raman spectroscopy, FT-IRspectroscopy, optical microscopy, porosity measurements, densitymeasurements, and the like. In one aspect, the inorganic phosphateprepared in accordance with the present disclosure as a density lessthan 1.8 g/cm³. In another aspect, the inorganic phosphate prepared inaccordance with the present disclosure as a density less than 1.5 g/cm³.

In another aspect, the instant corrosion resistant coatings can beformulated to provide aesthetic properties, such as color, proper shine,and texture. This effect may be achieved, for example, by addingpigments, color aggregate, crushed glass, sand, etc., to the instantacidic phosphate/alkaline metal oxide/hydroxide formulations. Forexample, the resulting coating comprising crushed glass prepared by theprocesses disclosed herein provides a very dense glassy surface.Additional suitable ceramic pigments may be further added to producecolored paints. Soluble glass in combination with the instantcompositions above can also be used in formulations for coating of solidobjects, to provide very dense, glassy solid coatings having corrosionresistance.

Experimental Section

The following examples are illustrative of the embodiments presentlydisclosed, and are not to be interpreted as limiting or restrictive. Allnumbers expressing quantities of ingredients, reaction conditions, andso forth used herein may be understood as being modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth herein may beapproximations that may vary depending upon the desired propertiessought to be obtained. At the very least, and not as an attempt to limitthe application of the doctrine of equivalents to the scope of anyclaims in any application claiming priority to the present application,each numerical parameter should be construed in light of the number ofsignificant digits and ordinary rounding approaches. Severalexperimental examples, listed below, were conducted in order toformulate, coat, and demonstrate the attributes of the instantcompositions disclosed herein.

A range of phosphate compositions may be used as the corrosion inhibitorcoatings commensurate with the spirit and scope of that disclosed anddescribed herein, the following exemplary, non-limiting examples areprovided:

TABLE 1 Exemplary Phosphate Ceramic Compositions Part A Part B SampleWeight percent (%) of Part A Weight percent (%) of Part B A monopotassium phosphate magnesium hydroxide (MKP) (~63-64%) of (~38-39%) anaverage particle size wollastonite (~20-21%) of about 20 micron xanthangum (0.07%) phosphoric acid (~8%) remainder water ~27-28% xanthan gum(0.15%) crystalline SiO₂ (~1.5%) remainder water B Mono PotassiumPhosphate magnesium hydroxide (MKP) (~63-64%) of (~40%) an averageparticle size xanthan gum (0.07%) of about 20 micron K₃PO₄ (~3.5%)phosphoric acid (~6%) remainder water xanthan gum (0.15%) crystallineSiO₂ (~1%) calcined kaolin (~12%) remainder water Control mono potassiumphosphate magnesium hydroxide (MKP) (~63-64%) (~38-39%) average particlesize wollastonite (~20-21%) about 200-700 microns xanthan gum (0.07%)phosphoric acid (~8%) remainder water ~27-28% xanthan gum (0.15%)crystalline SiO₂ (~1.5%) remainder water

Samples A and B and Control when field tested on storage tanks showedthat the Control samples containing larger average particle size MKPwere more likely, if not consistently, prone to pitting, galling,cracking, and staining that was visible upon inspection after fourmonths. In contrast, Samples A and B, using smaller average particlesize MKP, did not show visible signs of coating-induced corrosion orpitting and further, provided excellent resistance toenvironmentally-caused corrosion events such as salt spray, rain, andhumidity.

1. A phosphate ceramic precursor composition comprising: a firstcomponent comprising an aqueous mixture of an acid-phosphate of chemicalformula A^(m)(H₂PO₄)_(m).nH₂O, where A is hydrogen ion, ammonium cation,metal cation, or mixtures thereof; where m=1-3, and n=0-6; the firstcomponent solution adjusted to a pH of about 2 to about 5, the firstcomponent having a particle size distribution between 0.04 to 60 micron;and a second component, configured for combination and at least partialreaction with the first component to provide a phosphate ceramic, thesecond component comprising an aqueous mixture of an alkaline oxide oralkaline hydroxide represented by B^(2m)O_(m), B(OH)_(2m), or mixturesthereof, where B is an element of valency 2m (m=1, 1.5, or 2) the secondcomponent solution adjusted to a pH of between 9-14.
 2. The phosphateceramic precursor composition of claim 1, wherein about 50 percent ofthe particle size distribution of the first component is particleshaving a particle size less than 50 microns, less than 40 microns, lessthan 30 microns, or less than 20 microns.
 3. The phosphate ceramicprecursor composition of claim 1, wherein about 90 percent of theparticle size distribution of the first component is particles having aparticle size less than 50 microns, less than 40 microns, or less than30 microns.
 4. The phosphate ceramic precursor composition of claim 1,wherein the first component average particle size is about 20 microns toabout 30 microns.
 5. The phosphate ceramic precursor composition ofclaim 1, wherein the first component comprises at least one of monopotassium phosphate and mono calcium phosphate, water, and optionallyabout 2 to about 10 wt % phosphoric acid, and wherein the secondcomponent is at least one of magnesium oxide, calcium oxide, magnesiumhydroxide, and calcium hydroxide, and water.
 6. (canceled)
 7. Thephosphate ceramic precursor composition of claim 5, further comprisingat least one of a mineral silicate, wollastonite, talc, amorphousmagnesium silicate, amorphous calcium silicate, diatomaceous earth,silicon dioxide, amorphous silicon dioxide, a rheologymodifier/suspending agent, the rheology modifier/suspending agent is atleast one of guar gum, diutan gum, welan gum, and xanthan gum present inan amount of 0.15-15 weight percent.
 8. The phosphate ceramic precursorcomposition of a claim 5, wherein either of the first component or thesecond component is present in an amount of at least about 60 wt % toabout 80 wt %.
 9. (canceled)
 10. A method of providing corrosionprotection to a metal surface, the method comprising: contacting a metalsurface with a first component and a second component, in any order orin combination; wherein the first component comprises an aqueous mixtureof an acid-phosphate of chemical formula A^(m)(H₂PO₄)_(m).nH₂O, where Ais hydrogen ion, ammonium cation, metal cation, or mixtures thereof;where m=1-3, and n=0-6; the first component solution adjusted to a pH ofabout 2 to about 5, the first component having a particle sizedistribution between 0.04 to 60 micron; and wherein the second componentcomprises an aqueous mixture of an alkaline oxide or alkaline hydroxiderepresented by B^(2m)O_(m), B(OH)_(2m), or mixtures thereof, where B isan element of valency 2m (m=1, 1.5, or 2) the second component solutionadjusted to a pH of between 9-14; and providing corrosion protection tothe metal surface.
 11. The method of claim 10, wherein about 50 percentof the particle size distribution of the first component is particleshaving a particle size less than 50 microns, less than 40 microns, lessthan 30 microns, or less than 20 microns.
 12. The method of claim 10,wherein about 90 percent of the particle size distribution of the firstcomponent is particles having a particle size less than 50 microns, lessthan 40 microns, or less than 30 microns.
 13. The method of claim 10,wherein the first component average particle size is about 20 microns toabout 30 microns.
 14. The method of claim 10, wherein the firstcomponent comprises a dihydrogen phosphate salt of formulaM^(m)(H₂PO₄)_(m) and its hydrates, or mixtures thereof; where M sodium,potassium, magnesium, calcium, aluminum, or mixtures thereof, and m is1-3.
 15. The method of claim 10, wherein the first component compriseswater, at least one of mono potassium phosphate and mono calciumphosphate, and optionally, about 2 to about 10 wt % phosphoric acid, andwherein the second component is at least one of magnesium oxide, calciumoxide, magnesium hydroxide, and calcium hydroxide, and water. 16.(canceled)
 17. The method of claim 10, wherein the second componentfurther comprises wollastonite, talc, Class C fly ash, Class F fly ash,kaolin clay, kaolinite, meta kaolin, mullite, calcium aluminateminerals, calcium silicate minerals, aluminum silicate minerals, calciumaluminum silicate minerals, or mixtures thereof, in a weight ratio ofbetween 1:0.05 to 1:6 of the second component.
 18. The method of claim10, wherein the first component or the second component is present in anamount of at least about 60 wt % to about 80 wt %.
 19. (canceled)
 20. Aproduct coated by the method of claim
 10. 21-25. (canceled)